The present application generally relates to dynamic control of cooling fan speed in a vehicle equipped with a prime mover, providing a method, an apparatus, and a system for reducing aerodynamic drag of vehicles by optimizing fan speed. A number of methods, systems, and apparatus have been developed for reducing the aerodynamic drag of vehicles in order to improve their fuel efficiency. However, such developments continue to suffer from a number of limitations and shortcomings, including complexity in operation or design, costly construction or implementation, and lack of interchangeability among different vehicle configurations. Therefore, a significant need remains for further improvements in systems, apparatus, and methods for reducing aerodynamic drag.